The present invention generally relates to a method for processing optical proximity correction, and more specifically, to a method for processing optical proximity correction with uniformity of the wafer surface in order to secure a process margin.
As the design rule is reduced due to increased integration of semiconductor devices, various researches for forming a fine pattern have been made.
Since the wavelength of exposure lights used in an exposing process becomes shorter, a pattern is not patterned according to a designed layout but is instead distorted.
As the pattern becomes smaller, a light strength of a specific pattern affects that of its adjacent pattern to cause an optical proximity effect where a pattern of the layout on the design has a different shape from that formed over a wafer.
The optical proximity effect needs to be compensated because it degrades performance of semiconductor devices. Optical proximity correction refers to correction of the layout to be formed over the wafer for compensation.
The optical proximity correction includes rule-based optical proximity correction for correcting the layout based on rules of mask layout correction, and model-based optical proximity correction for correcting the mask layout by predicting an image transcribed over the wafer based on mask pattern information and a wafer process condition.
For the model-based optical proximity correction, factors that cause the optical proximity effect should be considered. These factors include a process condition where a pattern of the designed layout is patterned over an actual wafer, and an exposed resulting structure.
In other words, these factors include exposure energy of an exposure light source, a focus and a topology of patterns formed over the wafer through an exposing process.
However, since the topology is measured only in consideration of the average thickness of a thin film of the wafer, variables generated from a chemical mechanical polishing (CMP) process or a deposition process cannot be verified accurately.
That is, since the topology is measured by the average thickness of patterns formed in the wafer, the topology is different in each region depending on the patterns. As a result, it is difficult to prevent collapse of the patterns in a region that is not exposed by the best focus because the focus is different.
Although the optimum condition is set for optical proximity correction, an optical proximity correction condition is different depending on the topology of the wafer, so that it is difficult to prevent damages generated in each region of the wafer.